*World of Mathematics*. ©2005-2006 Thomson Gale, a part of the Thomson Corporation. All rights reserved.

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A circle is defined as the set of all points in a plane that are a given **distance** from a fixed point in the plane. The fixed point is referred to as the center of the circle. The fixed distance, which is the distance from the center of the circle to any point on the rim of the circle, is called the radius. The center of the circle is considered a point of **symmetry**. Any line through it is called a line a symmetry. A circle has infinite lines of symmetry and one point of symmetry. Circles that have the same center, but not the same radius are called concentric circles.

The circle belongs to the group of curves known as **conic sections**. The circle can be shown as the intersection of a plane that is perpendicular to the axis of the cone and a right circular cone.

The...

This section contains 409 words(approx. 2 pages at 300 words per page) |